Motoi Okuda

A molecular dynamics study of chain configurations in n‐alkane‐like liquids

We present precise measurements of the configurational properties of n‐alkane‐like liquids with 4, 5, 8, 20, 50, and 100 methylene groups. Quantities measured include the distributions of square radii of gyration, square end‐to‐end distances and proportion of conformers. To achieve high precision for n=50 and 100 a Fujitsu AP 1000 massively parallel processing machine with up to 512 processors is used. The results are compared with those obtained for the Flory model of alkane chains in which only correlation between nearest‐neighbor torsion angles are considered; the latter were obtained by Monte Carlo sampling of isolated chains using the pivot algorithm. Discrepancies between the two sets of data are discussed in terms of solvent and end effects. For n=100 full configurational relaxation was not observed within 2 ns.

The preparation of polymer melt samples for computer simulation studies

We have previously proposed a method for preparing dense amorphous polymer samples which was designed to circumvent the need for long periods of relaxation to equilibrium [J. I. McKechnie, D. Brown, and J. H. R. Clarke, Macromolecules 25, 1562 (1992)]. In the current article, we examine in more detail the application of the method to the preparation of polymer melts using precise data from massively parallel simulations. We expose deficiencies in the original method and introduce a modification which improves the equilibration. The limitations of the overall procedure are discussed in detail.

A domain decomposition parallelization strategy for molecular dynamics simulations on distributed memory machines

Abstract An algorithm is described which allows large scale molecular dynamics simulations to be carried out on a distributed memory parallel computer. The method is a development of a spatial decomposition technique already described [S.Y. Liem, D. Brown and J.H.R. Clarke, Comput. Phys. Commun. 67 (1991) 261] but incorporates decomposition of 3-D space in all three dimensions with link-cell and neighbour table techniques for enhanced efficiency. It is shown that communications between processors can be minimized without incurring the penalties associated with redundant force calculations. The method has been tested on a Fujitsu AP1000 parallel machine with up to 512 processor elements.

Scaling study of pure gauge lattice QCD by Monte Carlo renormalization group method

The scaling behavior of pure gauge SU(3) in the region [beta]=5.85[minus]7.60 is examined by a Monte Carlo renormalization group analysis. The coupling shifts induced by factor 2 blocking are measured on both 32[sup 4] and 16[sup 4] lattices with high statistics. A systematic deviation from naive 2-loop scaling is clearly seen. The mean field and effective coupling constant schemes explain part, but not all, of the deviation. It can be accounted for by a suitable change of coupling constant, including a correction term [ital O]([ital g][sup 7]) in the 2-loop lattice [beta] function. Based on this improvement, [radical][sigma] /[Lambda][sub M[bar S]][sup [ital n]][sub [ital f]]=0 is estimated to be 2.2[plus minus]0.1 from the analysis of the string tension [sigma].

A domain decomposition parallel processing algorithm for molecular dynamics simulations of polymers

Abstract We describe in this paper a domain decomposition molecular dynamics algorithm for use on distributed memory parallel computers which is capable of handling systems containing rigid bond constraints and three- and four-body potentials as well as non-bonded potentials. The algorithm has been successfully implemented on the Fujitsu 1024 processor element AP1000 machine. The performance has been compared with and benchmarked against the alternative cloning method of parallel processing [D. Brown, J.H.R. Clarke, M. Okuda and T. Yamazaki, J. Chem. Phys., 100 (1994) 1684] and results obtained using other scalar and vector machines. Two parallel versions of the SHAKE algorithm, which solves the bond length constraints problem, have been compared with regard to optimising the performance of this procedure.

A large scale molecular dynamics study of chain configurations in the n=100 alkane melt

We describe simulations of a polymer melt sample containing 640 chains, each chain being composed of 100 methylene groups. Using these large scale simulations radii of gyration have been calculated with a statistical error of ∼2%. At this level of precision it is shown that even for this modest chain length configurational equilibrium is not achieved in less than 4 ns at 500 K. Values of the square radii of gyration, square end‐to‐end distances and proportion of conformers at equilibrium show good agreement with predictions of the Flory model of alkane chains in which all long range interactions along the chains are ignored. These simulations were performed using a Fujitsu AP1000 massively parallel processing machine with 1024 processors in conjunction with a recently described domain decomposition molecular dynamics algorithm [D. Brown, J. H. R. Clarke, M. Okuda, and T. Yamazaki, Comput. Phys. Commun. 83, 1 (1994)] capable of handling systems containing rigid bond constraints and threea are made with pre...

Spectral analysis of mesonic channels at finite temperature on anisotropic lattices

Abstract We study the spectral function of mesonic correlators at finite temperature. The mesonic correlators are measured along the “time” direction with fine lattice spacing on anisotropic lattices. A new method to construct a spectral function from a correlator is proposed. The temperature dependence of the shape of the mesonic spectrum is investigated.

Finite temperature gauge theory on anisotropic lattices

The finite temperature transition of QCD can be seen as a change in the structure of the hadrons and as a symmetry breaking transition -- a change in the structure of the vacuum. These phenomena are observed differently and carry complementary information. We aim at a correlated analysis involving hadronic correlators and the vacuum structure including field and density correlations, both non-trivial questions.

QCD on the highly parallel computer AP1000

Abstract We have been running quenched QCD simulations on 32 4 and 32 3 × 48 lattices using a 512 processor AP1000, which is a highly parallel computer with up to 1024 processing elements. We have developed programs for update, blocking and hadron propagator calculations. The pseudo heatbath and the overrelaxation algorithms were used for the update with performance of 2.6 and 2.0 μsec/link, respectively.

QCD on the massively parallel computer AP1000

We present the QCD-TARO program of calculations which uses the parallel computer AP1000 of Fujitsu. We discuss the results on scaling, correlation times and hadronic spectrum, some aspects of the implementation and the future prospects.